This invention relates to precision drives for industrial manipulators and, more particularly, to a new and useful pneumatic or air pressure drive by means of which an exact positioning of a mechanical member of the manipulator, having to perform either a translatory or rotary motion before reaching its final position, can be obtained.
At the present time, in cases where an accurate positioning of the working member of a mechanism and a sensitive control of the velocity of its motion toward the desired position is wanted, electric, hydraulic, or pneumatic drives are used. Such drives are needed in many different applications such as, for example, in industrial sewing machines. One of the most important applications of these drives, however, is in manipulators, particularly industrial manipulators. Such manipulators comprise members having to perform a rotary or linear translatory motion before coming to their position, the number of members corresponding to the number of degrees of freedom. Each member may be provided with its own separate drive.
In manipulators, the velocity and, in particular, the final positioning of the respective working member must be controlled in an exactly defined manner. Frequently, it is also necessary to control the whole movement of the working member along a path leading to the final position.
In view of their excellent properties and for economic reasons, pneumatic drives would be particularly suitable for use in manipulators and also for other applications, provided they could permit an accurate and simple positioning. However, conventional pneumatic drives use mechanical stops for the positioning and do not permit any programming or re-programming through a central control or a computer. Up to date, pneumatic drives are "programmed" with a monkey wrench. That is why, in an operational cycle, only the operative range between the stops, and not the range outside the stops, can be used. This is a considerable drawback.
Attempts have been made to control pneumatic or compressed air drives. In such cases, however, certain physical limits are reached very soon. Namely, the compressibility of air does not permit a free positioning without relation to the load, and the control of an air cylinder is very difficult because of the high time constant of the cylinder spaces acting as accumulators during the charging and discharging operation.
The present invention is directed to eliminating the mentioned disadvantages of a pneumatic drive and to make it suitable for precision positioning.